Light emitting diodes (LED) as light sources are becoming more and more popular, as they are more power-efficient than incandescent lights and fluorescent lights. However, the light emitting area of an LED is usually very small and is regarded as a point light source. Light is highly concentrated at the point light source and spreads into all directions. It is too bright for a human eye to directly look at the source. Therefore, there is a need to attain a uniform light profile.